1. Field of the Invention
The present invention relates to a shape-of-endoscope detecting apparatus for detecting the shape of a portion of an insertion unit of an endoscope inserted into a body cavity using magnetic fields, and for graphically indicating the shape in a characteristic manner, and to a shape-of-endoscope detecting method using the apparatus.
2. Related Art Statement
In general, endoscopes can be used to observe a lesion or perform required treatment on the lesion with an elongated and flexible insertion unit thereof inserted externally into a lumen in a human body.
Lumens including the large intestine and small intestine are tortuous. An operator of the endoscope is therefore unaware of to where the insertion unit of the endoscope has been inserted or what shape the insertion unit now assumes.
For inserting the insertion unit, the work of insertion, including angling of a bending portion of the insertion unit to follow the twists, bends, or turns of the lumen must be performed smoothly. From this viewpoint, if it can be learned where in a body cavity the distal part of the insertion unit is located or how the insertion unit is now bent, it would be convenient.
The present applicant has proposed in Japanese Patent Application No. 10-69075 an apparatus for detecting the inserted state of an endoscope or a catheter. The detecting apparatus can detect the inserted state of an insertion unit of the endoscope in a human body using magnetic fields without affecting the physiological condition of the human body. Using the apparatus, a user rotates the inserted portion of the endoscope so that he/she can easily observe the shape of the inserted portion.
However, according to the foregoing related art, the shape of the endoscope is not graphically indicated so that the user can clearly recognize the positional relationship among the endoscope, an intracorporeal region of a patient, and an extracorporeal region thereof. Consequently, the positional relationship between the endoscope and intracorporeal region is hard to ascertain. In other words, the position in a patient body to which the insertion unit of the endoscope has been inserted is hard to discern. Besides, if the insertion unit is located outside a detectable range, the position of the insertion unit may be detected incorrectly and the shape of the insertion unit may be graphically indicated to be at a set of coordinates defined on a monitor which is offset from the correct point.
Moreover, even if it can be discerned that the endoscope has been inserted into an intracorporeal region, the absolute length of the inserted portion of the endoscope is uncertain. This poses a problem in that it is hard to discern in what intracorporeal region in a patient, body the insertion unit of the endoscope lies. It is therefore desired to achieve an improved apparatus which helps to enable the insertion unit of the endoscope to be inserted smoothly.
Furthermore, according to the display method employed in the related art, even if a user sets a viewing point so that he/she can easily observe the shape of an inserted portion of an endoscope, once a patient changes his/her posture; there is no means enabling the user to determine the patient's posture. Since the position and angle of the graphically indicated shape of the insertion unit will vary with the patient's posture, the related art therefore has the drawback in that the user must re-set the viewing point. Incidentally, the viewing point is such that the shape of the inserted portion is graphically indicated while being depicted as if the inserted portion were viewed from the viewing point.
Moreover, the whole display screen is used to graphically indicate the shape of an endoscope. An area not of interest to the user, for example, an area outside the patient's body may also be graphically indicated. The user therefore has to identify on the screen the region he/she wants to observe carefully, for example, a patient's intracorporeal region.
Furthermore, the insertion unit of the endoscope to be inserted into a body cavity has a bending portion “made by concatenating a plurality of metallic bending pieces so that the pieces can freely rotate. Magnetic fields induced by source coils are affected by the pieces. When the bending portion is angled, the bending pieces move. Consequently, the shape of the bending portion changes. This disturbs the magnetic fields induced by the source coils, so that sets of coordinates specifying positions in the insertion unit cannot be defected accurately. This generates a concern that it may become impossible to graphically indicate on the screen the shape of the insertion unit with high precision.
Moreover, some source coils are incorporated in the bending portion: When the bending portion is angled, the source coils may hit the bending pieces or other structural elements of the insertion unit and thus interrupt bending. Moreover, there is a concern that those structural elements or the source coils themselves may be damaged.
In addition, for example, Japanese Unexamined Patent Application Publication No. 8-107875 has disclosed a shape-of-endoscope detecting apparatus including source coils that induce a magnetic field and are arranged at predetermined intervals, and sensing coils that sense a magnetic field and are located in the vicinity of the patient. Signals produced by the sensing coils are used to detect the location of the source coils. The location information of the source coils is used to calculate three-dimensional data representing the shape of the insertion unit. The three-dimensional data is transformed into two-dimensional data representing the shape of the insertion unit as if the insertion unit were viewed from a predetermined viewing point. The shape of the insertion unit is then graphically indicated on a monitor. The published patent application identified above has thus disclosed a technology for making it possible to determine the shape of an insertion unit that is not visible to the operator using the endoscope, and for improving the maneuverability of an endoscope.
The shape-of-endoscope detecting apparatus makes it possible to determine the shape of an inserted portion of the endoscope and thus contributes to improving the maneuverability of the endoscope. However, the insertion unit of the endoscope may be used for being inserted into a tortuous lumen. Therefore, when, for example, the bending portion is angled, it is not easy to determine, based on the shape of the insertion unit graphically indicated on the monitor, in which direction the distal part of the insertion unit will actually be moved. In other words, when the shape of the insertion portion is merely graphically indicated on the monitor, special expertise is needed to accurately determine the relationship between, the manipulation performed on the endoscope and the position of the inserted portion of the endoscope.